Control device



Patented Mar. 13, 1945 I CONTROL DEVICE Willis H. Gille, St. Paul, and Harold A. Petsch,

ssignors to Minneapolislloneywell Regulato Company, Minneapolis, Mi nn., a corporation of Delaware Application August 6, 1942, Serial No. 453,914

Minneapolis, Minn.,

2 Claims.

The present invention relates to control apparatus, and more particularly to electrical followup arrangements of the type wherein a device icsponsive to a variable condition operates to produce an electrical signal variable in accordance with the changes of the condition, and wherein the electrical signal so produced is used to actuate suitable control devices.

An object of the present invention is to produce a transmitter device for an electrical control system, which may be readily operated by a condition responsive device of low power characteristics.

Another object of the-invention is to construct an improved variable impedance transmitter device for an electrical control system comprising a stationary member and a movable armature member. A further object is to provide in such a device an armature structure which is movable by low powered condition responsive means, and which is supported by means other than the condition responsive means.

By the term condition responsive device" as used herein is meant any control device which automaticall responds to any variable condition or force. While we have disclosed our invention asapplied to a system wherein temperature is the controlling condition, it is equally applicable to systems wherein the controlling condition may be, for example, the position of a movable memher, or a force such as gravity or the force due to a magnetic field.

Another object of the invention is to provide, in an electromagnetic transmitter device wherein an armature is moved'into engagement with a Figure 1 represents, somewhat diagrammatically, a control system utilizing a preferred embodiment of my invention, and

Figure 2 is a cross-sectional view taken along the line 2-2 of Figure 1, looking in the direction of the arrows.

In the drawing is shown a valve Ill, which may, ,for example, control a supply of temperature changing fluid such as steam, and which is controlled in accordance with the temperature existing adjacent a thermostat II, which is shown as being of the fluid filled bellows type.

Valve H) is provided with a stem l2, upon which is mounted a rack I3. A pinion l4, engageable with the rack I3, is driven by a motor generally indicated at l5 through a gear train shown diagrammatically at |6. Motor |5 also drives, through the gear train Hi, a slider 20 which is movable with respect to a slidewire resistance 2|.

Motor I5 is shown as being of the split phase type, having a pair of field windings 22 and 23 which are 90 degrees apart in space phase. Winding 22 is continuously energized from a secondary winding 24 of a transformer 25. A condenser 26 is connected in series between the secondary winding 24 and the motor winding 22.

Transformer 25 has a primary winding 21 and another secondary winding 28.

Motor winding 23 is energizable from secondary winding 28, energization thereof being controlled by an electronic amplifier 30, which may be for example an amplifier 01" the type shown and described in the copending application of Albert P. Upton, Serial No. 437,561, dated April 3, 1942. Amplifier 30 is provided with input terminals 3| and 32 and output terminals, 33 and 34. Power for the final output stage of amplifier 30 is supplied from secondary winding 28, while power for other parts of the amplifier circuit is supplied from a secondary winding 35 of a transformer 36 having a primary winding 31.

Amplifier input terminals 3| and 32 are connected b'y conductors 4| and 42, respectively, to

output terminals 43 and 44 of an impedance bridge circuit generally indicated at 45. Output terminal 44 is the point of engagement of slider 20 with slidewire 2|. The bridge circuit 45 has input terminals 46 and 41 connected to a secondary winding 48 of a transformer 49 having a primary' winding 50.

Unbalance of the bridge circuit 45 is controlled by a variable impedance device generally indicated at 5|. The variable impedance device 5| includes a stationary'core member 52, of a generally E shaped configuration. On the left and right legs of the coremember 52, impedance coils 53 and 54, respectively, are mounted. The core member 52 may preferably be laminated, as indicated in Figure 2. Attached to the center leg of the core'member 52, are a 'pair of bracket plates 60. which are attached to the core member 52 by any suitable moans such as the screws The upper ends of the plates are offset from the core member 52, and carry stationary bearings 55 and 56. The bearing 56 threadedly engages the plate 60, so that the tightness of the bearing assembly may beadjusted.

Pivotally supported in the bearings 55 and 56, is a generally E shaped armature member 51. The bearings 55 and 56 engage the armature member 51 at a point on the center leg of the E. The armature member 51 is therefore substantially balanced about its pivotal support. The outer legs of the armature member 51 are extended toward the outer legs of the stationary core member 52. When the armature member 51 pivots about the bearings 55 and 56, the outer legs move towards and away from the stationary core member 52. The surfaces of the outer legs of the armaturemember 51 which extend toward the outer legs of the stationary core member 52 are provided with plates 62 of copper or other electrically conductive, non-magnetic material to prevent any sticking of the armature to the stationary core member.

The armature member 51 carries a pin 63. Pin.

63 is engaged by a yoke 64 mounted on one end of a lever 65, whose opposite end is pivoted to a fixed support.

A pin 66 attached to the top of the thermostatic bellows engages a portion of lever 65 so as to cause rotation thereof. A tension spring 61 has one end attached to the lever 65 and its opposite end fixed, so as to bias the lever 65 into engagement with pin 66 on thermostat I The upper left arm of bridge circuit 45 connects input terminal 46 with output terminal 43, and' includes a conductor 10, coil 53, and a conductor 1|. The upper right arm of bridge circuit 45.con-

nects output terminal '43 with input terminal 41,

and includes a conductor 12, coil 54, and a conductor 13.

The lower left arm of bridge circuit 45 connects input terminal 46 and output terminal 44, and includes a fixed resistance 14,-a conductor 15, and that part of slidewire resistance 2| between its left-hand terminal and its point of engagement with slider 20.

The lower right arm of bridge circuit connects input terminal 41 with output terminal 44 and includes a fixed resistance 16, a conductor 11,.

and that portion of slide-wire resistance 2| between its right-hand terminal and its point of engagement with slider 20.

A variable resistance 5. is connected across the slidewire resistance 2| in order that the ratio between a given unbalance effect of the bridge and the amount of movement of slider 20 necessary to restore balance to the bridge may be adjusted, in a manner well known in the art.

A condenser 8| is connected across the terminals of motor winding 23, and is proportioned with respect to winding 23 to provide a series resonant 100p circuit of low impedance therethrough, so as to facilitate the flow of current induced in winding 23 by transformer action from winding 22.

Referring to the variable impedance device 5|, it may be observed that the electrical connections to the coils 53 and 54 are such that the magnetic flux produced by both coils is of the same polarity at any instant. It is assumed that both coils are wound in the same direction. In other words, when the flux produced by coil 53 is downward in direction, the flux produced by coil 54 is also downward. Each coil may therefore be said to produce a flux which tends to oppose the flow through that coil of flux produced by the other coil. 3

The magnetic circuit of the fluxproducdzibyi i coil 53 may be. traced (assuming the flux direction to be downward) through the left leg of core member 52, to the right along the yoke portion of member 52, up through the center leg across the air gap adjacent the bearings 55 and 56 to armature member 51, to the left along member 51, down through its left leg and across the air gap to the left leg of core member 52.

The magnetic circuit of the flux produced by Icoil 54 may be traced (assuming the direction downward) through the right leg of core member 52, to the-left along the yoke portion of member 52, up through the center leg, across the air gap adjacent bearings 55 and 56 to armature member 51, to the right along member 51, down through its right'leg and across the air gap to the right leg of member 52.

Operation way open. Under these conditions, let is be assumedthat the temperature adjacent the thermostat rises.

A rise in temperature adjacent the thermostat causes the gas or vapor therein to expand, pushing the pin 66 upwardly and rotating lever in a clockwise direction about its pivot. This motion of lever 65 acts through yoke 64 and pin 63, causing rotation of armature member. 51 in a counterclockwise direction about the bearings 55 and 56. This decreases the air gap in the magnetic circuit of the flux produced by the coil 53, and increases the air gap in the magnetic circuitof the flux produced by the coil 54. The flux threading the coil 53 therefore increases, increasing the impedance of the coil 53. On the other hand, the flux through the coil 54 decreases, decreasing the impedance of that coil.

Referring now to the bridge circuit 45, it will I be seen that when the impedance of coil 53 increases and the impedance of coil 54 decreases, the potential of output terminal 43 is shifted from a value exactly half-way between that of input terminals 46 and 41 to a value somewhat closer to that of input terminal 41. Therefore, a potential difference exists between output terminals 43 and 44, and the phase of this potential difference is the same as if' terminal 43 were connected to terminal 41 and terminal 44 were connected to input terminal 46. In other words, it may be stated that the phase of the potential appearing at terminals 43 and is opposite to the phase of the potential applied to the terminals 46 and 41. This potential difference is fed through conductors 4| and .42 to input terminals 3| and 32 of amplifier 30.

As described in detail in the copending Upton application previously referred to, the amplifier 30 is of a type which produces in the output circuit including conductor 29 and motor winding 23 an alternating current whose phase is dependent upon the phase of the potential applied to input terminals 3| and 32. The current flowing through winding 22 is of substantially constant phase, as determined by the relative impedances of condenser 26 and winding 22. The winding 23, on the 7 other hand, is supplied with current which either leads-or. lags the current in winding 22 by approximately electrical degrees, depending upon the direction of unbalance of bridge circuit 45.

In accordance with the well known characteristics of a split phase motor, when the windings 22 and 23 are supplied with current substantially 90 degrees out of phase, the motor I! is caused to rotate in a predetermined direction depending upon which current leads the other. In the present instance, the direction will be such as to rotate slider 20 in a clockwise direction, thereby moving output terminal 44 of bridge 45 to the right along slidewire resistance 2| and decreasing the difierence in potential between output terminals 43 and 44. At the same time, the motor l5 drives the pinion l4 in a direction so as to move the valve ll) towards its closed position.

As slider moves to the right along slidewire resistance 2!, it reaches a point where the potential of output terminal 44 exactly equals that of output terminal 43, and the bridge circuit is again balanced. No signal is then applied to' the input terminals 3| and 32 of amplifier 30. winding 23 of motor I 5 is no longer energized, and therefore the motor stops.

In a similar manner, it, with the parts in the position shown in the drawing, the temperature adjacent the thermostat ll decreases, the lever is rotated counter-clockwise, thereby causing rotation of armature member 51 clockwise. This decreases the air gap in the right leg of the impedance device 5|, and increases the air gap in the left leg, thereby increasing the impedance of coil 54 and decreasing the impedance of coil 53. Bridge circuit 45 is then unbalanced in the opposite sense, the potential of output terminal 43 being shifted toward that of input terminal 46. A potential difference then exists between output terminals 43 and 44 which is of the same phase as the potential applied to input terminals 46 and 41. This potential is applied to amplifier input terminals 3| and 32 and causes the production of a current in the motor winding 23. Motor windings 22 and 23 are again energized with current differing in phase by degrees, b it the phase relationship between these two currents opposite, that is, the current which was leading before is now the lagging current, and therefore rotation of motor is takes place in the opposite direction. This rotation of motor I! drives slider 20 in a counter-clockwise direction so as to move terminal 44 to the left along slidewire resistance 2| and rebalance the circuit 45. At the same time, pinion I4 is rotated in a proper direction to cause opening of the valve I0.

Referring to the impedance device 5|, it will be seen that we have provided an improved variable impedance device for producing an alternating electrical signal variable in accordance with the characteristics of a variable condition. Furthermore, the power which must be supplied by the sensitive element to operate the device 5| is very small, and the movable portion of the device 5| is supported by means other than the condition responsive element. It should also be apparent that Lhave provided a magnetic pickup arrangement for an electronic amplifier which is not subject to the influence of stray magnetic fields, inasmuch as any stray fields existing in the neighborhood of the impedance device 5| would produce equal effects in windings 53 and 54.

While we have shown and described a preterred embodiment of our invention, other modifications thereof will readily occur to those skilled in the art, and we therefore wish our invention to be limited only by the definitions set forth in the appended claims.

We claim as our invention:

1. In an electrical bridge arrangement for producing an alternating electrical signal variable in phase and magnitude in accordance with the direction and magnitude of departure of a variable condition from a predetermined value, a source of alternating potential, a pair of series connected impedance arms connected to said source, and a variable reactor including a pair of series connected coils also connected to said source of potential in parallel with said pair of impedance arms so that the junctions of said impedancearms and said coils constitute the output terminals of said bridge arrangement, said variable reactor comprising a substantially E-shaped core member of magnetic material having a center leg and'a pair of outer legs, said coils being disposed on each of the outer legs, an armature member rotatable about a point aligned with said center leg, said armature and said legs of said core member each having a pair of contacting portions for cooperating with those of the other member, means for preventing magnetic engagement of said contacting portions, and means responsive to said variable condition for causing relative rotation between said armature and core members thereby to oppositely vary the spaces between said outer legs and said armature portions and thus unbalance said bridge arrangement to produce at said output terminals an alternating voltage of the frequency of said source and having a phase relation and magnitude dependent upon the value of said condition.

2. In an electrical bridge arrangement for producing an alternating electrical signal variable in phase and magnitude in accordance with the direction and magnitude of departure of a variable condition from a predetermined value, a source of alternating potential, a pair of series connected impedance arms connected to said source, and a variable reactor including a pair of series connected coils also connected to said source of potential in parallel with said pair of impedance arms so that the junctions of said impedance arms and said coils constitute the output terminals of said bridge arrangement, said variable reactor comprising a substantially E-shaped core member of magnetic material having a center leg and a pair of outer legs, said coils being disposed on each of the outer legs, an E-shaped armature member rotatable about a point aligned with said center leg, said armature and said legs of said core member each having a pair of contacting portions for cooperating with those of the other member, at least one of the pairs being of non-magnetic material, and means responsive to said variable condition for causing relative rotation between said armature and core members thereby to oppositely vary the spaces between said outer legs and said armature portions and thus unbalance said bridge arrangement to produce at said output terminals an alternating voltage of the frequency of said course and having a phase relation andmagnitude depending upon the value of said condition.

WILLIS H. GILLE. HAROLD A. PETSCH. 

